The present invention relates to a process for the selective additive correction of voids in copying layers of printing plates and conductor boards utilizing an aqueous electrolyte solution.
In the preparation of offset printing plates or photoresists (both referred to hereinafter as copying materials) radiation-sensitive (light-sensitive) reproduction layers are used, that, in general, are applied to a support by the customer or industrial manufacturer. The layer supports used in such copying materials include metals such as zinc, magnesium, chromium, copper, brass, steel, silicon, aluminum or combinations of these metals, plastic films, paper or similar materials. These supports can be coated with the radiation-sensitive reproduction layer without a modifying pretreatment, but preferably after carrying out a surface modification such as mechanical, chemical and/or electrochemical graining, surface oxidation and/or treatment with agents which impart hydrophilicity (for example, in the case of supports for offset printing plates). In addition to at least one radiation-sensitive compound, the conventional radiation-sensitive reproduction layers usually also contain an organic binder (e.g., resins) and, optionally, also plasticizers, pigments, dyes, surfactants, sensitizers, adhesion promoters, indicators and other customary auxiliary agents. In order to produce an image from these reproduction layers, the layers are developed after their irradiation(exposure) to obtain, for example, a printing form or a photoresist. In the case of electrophotographic layers, the step of decoating corresponds to the developing step. Within the scope of this invention, the term "reproduction layers" also includes layers that do not contain a radiation-sensitive compound, but contain the other above-mentioned components, i.e., in particular an organic binder.
The prior art has disclosed processes in which it is possible to produce a printing form without an irradiation and/or developing step and thus without using the customary reproduction layers containing a radiation-sensitive compound.
German Patent No. 24 33 448 (=U.S. Pat. No. 4,086,853) discloses the use of an electro-responsive recording blank comprising a) a hydrophobic underlayer (for example, of polyester), b) an electrically conductive hydrophilic layer (for example, of aluminum) arranged thereon, which can be locally removed by the action of current by means of a stylus, and c) a layer (composed, for example, of a cellulose derivative, a plasticizer and a pigment) that, as a result of the action of electric current, can be removed from layer b).
German Offenlegungsschrift No. 25 14 682 (=British Patent No. 1,490,732) describes the use of an electroresponsive recording material comprising a) an electrically conductive oleophilic layer which cannot be removed by the action of electric current and b) an oleophobic silicone rubber layer arranged thereon which can be locally removed by the action of current by means of a stylus.
Furthermore, European Patent Application No. 0,030,642 discloses a process for producing, by electroerosion, a printing form from a sheet-like material, comprising (a) a hydrophobic substrate layer (for example, of polyester), (b) a hydrophilic, electrically conductive intermediate layer (for example, of aluminum) and (c) a protective dielectric top layer (for example, of Al.sub.2 O.sub.3), in which process both layers (c) and (b) are removed by the action of electrodes.
These prior art processes are based on an imagewise removal of layer components by electrochemical degradation.
European Patent Application No. 0,155,231 describes electro dipcoating of a printed circuit board that, after coating, is processed by imagewise exposure and development.
According to European Patent No. 0,089,510 (=U.S. Pat. No. 4,376,814) a hydrophilic polymer is electrochemically deposited on a printing plate.
It is true that, in the two processes, polymers are deposited by electro dipcoating, but imagewise differentiation is not used in these processes.
Imagewise differentiation is described in the following publications:
U.S. Pat. No. 4,519,876 discloses an electrically conductive substrate carrying an insulating layer which can be removed imagewise after exposure to laser energy. Thereafter, metal is electrolytically deposited in the exposed regions which are no longer protected.
In Japanese Patent Application Disclosure No. 51-078,406 an analogous process is described, in which a screen printing mask is used as an original and metal is electrodeposited in the uncovered portions of the screen.
In addition, the patent literature has disclosed processes wherein deposits are produced by an electrophotographic route or by means of conductivity patterns.
U.S. Pat. Nos. 3,106,157 and 3,085,051, for example, describe processes, in which the conductivity pattern produced by imagewise exposure serves to deposit indium or nickel atoms.
U.S. Pat. No. 3,095,808 describes the utilization of photoconductivity after imagewise exposure for depositing a Fe, Cu, Ni or Co salt of rubeanic acid.
According to U.S. Pat. No. 3,106,155 a photoconductivity pattern created by imagewise exposure is "developed," by means of polymers, for example, by cellulose acetate phthalate.
In all these processes imagewise exposure must first be carried out to produce a conductivity pattern which is fixed in further process steps.